Airboats have long been used for travel upon swamps and other shallow bodies of water. Such boats are generally catamaran like structures having two hulls or pontoons, and are equipped with aircraft type propulsion such as an air fan propeller located on the deck of the boat. This design enables the airboat to travel in shallow waters that are not navigable by vessels having a conventional immersed propeller. U.S. Pat. No. 6,148,757 discloses an airboat having the catamaran hulls designed for guiding water outward and under the hulls to move contact of the hulls with the water surface aft. This decreases hull drag and increases lift at higher speeds. However, the lift is only variable by changing the speed of the airboat. An airboat of this design requires a long distance to achieve higher speeds and is restricted for travel over smooth surfaces, i.e. mostly water surfaces.
Other types of air-driven boats include aerodynamic surface effect vessels, which with forward motion, develop a ram air lifting force by funneling and compressing a high velocity air stream within a channel defined by at least two hulls, a deck and water surface, as disclosed, for example, in U.S. Pat. Nos. 3,799,095 and 6,058,872. The surface effect lift is capable of raising a vessel a relatively small distance above an underlying substantially flat surface at higher speeds. U.S. Pat. Nos. 6,325,011 and 6,581,536 disclose high-speed air-supported crafts capable of operating as both a water-contacting craft and a wing in ground effect aircraft. However, these crafts require relatively long distances of a smooth surface such as a calm water surface in order to achieve the high speeds necessary for providing lift. Therefore, employment of such crafts is limited to situations where a calm water surface or a runway is available rendering them unsuitable for employment in numerous situations.
In order to overcome this limitation U.S. Pat. No. 5,464,069 describes an air-driven craft that combines aerodynamic lift with a hovercraft effect. In said hovercraft effect powerful fans produce an aircushion under the craft without forward motion for lifting the craft off the surface. However, the additional mechanism for generating the aircushion substantially increases the complexity as well as size and weight of the craft.
It would be advantageous to provide a surface effect craft that is capable of achieving aerodynamic lift at low speed. It would be further advantageous to provide a surface effect craft capable of adjusting aerodynamic lift in a wide operational range.